1. Field of the Invention
The invention relates to an improved method for the preparation of unsaturated alcohols and/or esters thereof by reacting conjugated dienes with water and/or aqueous carboxylic acid solutions in the presence of a macroporous acid ion exchanger.
2. Description of the Prior Art
Unsaturated alcohols and esters thereof are desirable intermediate products which play an important part, for example, in the synthesis of natural products such as terpenes. Therefore, there have been a number of attempts to find advantageous processes for their preparation. Thus, for example, the addition of carboxylic acids to conjugated dienes was examined in the presence of sulfuric acid (compare Ber. 76, (1943), 831) and catalysts such as PdCl.sub.2 /CuCl.sub.2 (compare the Bulletin of the Japanese Petroleum Institute 13 (1971) 73, Austrian Journal of Chemistry 1571, (1971), 24). However, the reactions are very nonspecific.
Another known method for the preparation of 2-methyl-3-butene-2-ol is the addition of hydrogen chloride to isoprene whereupon the reaction products are hydrolyzed in an alkaline medium (compare German Published Application 30 21 414), or a neutral medium (compare German Application 23 19 761). Drawbacks of these methods are the large salt production, multiple stages of the preparation process, as well as very pronounced corrosion problems.
Another method is known according to which 2-methyl-3-butene-2-ol is produced by reaction of acetylene with acetone and subsequent partial hydrogenation (compare M. De Malde, Chim. e Ind. (Milan) 45 (1963), page 665 and the following). However, acetylene is expensive and technically not simple to handle.
Also described in the prior art is the two-phase reaction of isoprene with water in tetrahydrofuran (THF) in the presence of the gel ion exchanger Amberlite.RTM. IR 120 (compare Bulletin of the Institute of Chemical Research, Kyoto University 1972, 50 (4), pages 863-7). However, in spite of temperatures of 80.degree. to 110.degree. C. and reaction times of up to 10 hours, this method resulted only in reactions of 7 percent maximum.
Therefore the purpose of this invention was to improve the method for the preparation of unsaturated alcohols and esters thereof by reacting conjugated dienes with water and/or with aqueous carboxylic acid solutions in such a manner that the desired compounds are achieved in a simple manner and with good yield in a single-stage process.
Surprisingly, it was found that the mentioned reaction at low temperatures with shorter reaction times results in a considerably higher reaction and higher yield than in the known method if the reaction is carried out in a homogeneous or quasi-homogeneous phase with suitable solvents in the presence of a macroporous acid ion exchanger.